Referring now to FIG. 1, an exemplary data storage device 10 is shown. A buffer 18 stores data that is associated the control of a hard disk drive. The buffer 18 may employ SDRAM or other types of low latency memory. A processor 22 performs processing that is related to the operation of the hard disk drive. A hard disk controller (HDC) 26 communicates with the buffer 18, the processor 22, a host 24, a spindle/voice coil motor (VCM) driver 30, and/or a read/write channel circuit 34.
During a write operation, the read/write channel circuit or read channel circuit 34 encodes the data to be written onto the storage medium. The read/write channel circuit 34 processes the signal for reliability and may include, for example error correction coding (ECC), run length limited coding (RLL), and the like. During read operations, the read/write channel circuit 34 converts an analog output from the medium to a digital signal. The converted signal is then detected and decoded by known techniques to recover the data written on the hard disk drive.
One or more hard drive platters 52 include a magnetic coating that stores magnetic fields. The platters 52 are rotated by a spindle motor that is schematically shown at 54. Generally the spindle motor 54 rotates the hard drive platter 52 at a fixed speed during the read/write operations. One or more read/write arms 58 move relative to the platters 52 to read and/or write data to/from the hard drive platters 52. The spindle/VCM driver 30 controls the spindle motor 54, which rotates the platter 52. The spindle/VCM driver 30 also generates control signals that position the read/write arm 58, for example using a voice coil actuator, a stepper motor or any other suitable actuator.
A read/write device 59 is located near a distal end of the read/write arm 58. The read/write device 59 includes a write element such as an inductor that generates a magnetic field. The read/write device 59 also includes a read element (such as a magneto-resistive (MR) element) that senses the magnetic fields on the platter 52. A preamplifier (preamp) circuit 60 amplifies analog read/write signals. When reading data, the preamp circuit 60 amplifies low level signals from the read element and outputs the amplified signal to the read/write channel circuit 34. While writing data, a write current that flows through the write element of the read/write device 59 is switched to produce a magnetic field having a positive or negative polarity. The positive or negative polarity is stored by the hard drive platter 52 and is used to represent data.
Referring now to FIG. 2, the read channel circuit 34 outputs write signals wdx and wdy to the preamp circuit 60 when writing data. The preamp circuit 60 amplifies the write signals using a write amplifier 90. The amplified write signals are output to the read/write device 59. When reading data, the preamp circuit 60 receives signals from the read/write device 59, amplifies the signals using a read amplifier 92 and outputs amplified read signals rdx and rdy to the read channel circuit 34. In current data storage device architectures, there is no way to test whether the preamp circuit 60 is operating properly. Therefore, it is difficult to diagnose malfunctions in the preamp circuit 60.